1. Field of the Invention
This invention relates to additives for use with the Mediterranean fruit fly attractant, trimedlure, 1,1-dimethylethyl 4(and 5)-chlorotrans-2-methylcyclohexanecarboxylate. In particular, it relates to certain esters of 4(and 5)-chloro-trans-2-methylcyclohexanecarboxylic acid and their ability to act as inhibitors to the formation of crystalline masses in trimedlure as well as their ability to extend the attractive duration of trimedlure when mixed with the attractant.
2. Description of the Art
The Mediterranean fruit fly [Ceratitus capitata (Wiedemann)] commonly known as the medfly, is one of the worst pests of stonefruit and citrus fruits and vegetables, and presents a major threat to fruit and vegetable production in areas with mild winters. Although infestations of the medfly are primarily in Hawaii and subtropical regions of the continent, periodic invasions onto the mainland United States have resulted in great economic losses.
Insect attractants have proved to be invaluable tools for the control of insect species. Beroza et al. (Agricultural and Food Chemistry 9(5): 361-365 (1961)) reported that certain esters prepared from a mixture of the isomeric acids 4(and 5)-chloro-trans-2-methylcyclohexanecarboxylic acid were superior attractants for the medfly. First medlure, 1-methylpropyl 4(and 5)-chloro-trans-2-methylcyclohexanecarboxylate, then trimedlure, 1,1-dimethylethyl 4(and 5)-chlorotrans-2-methylcyclohexanecarboxylate, were utilized by Federal and state agencies as the standard survey and detection lure for the medfly in replacement of siglure, 1-methylpropyl trans-6-methyl-3-cyclohexenecarboxylate. Trimedlure has also been used for many years as the standard medfly attractant wherever the fly is or threatens to become established worldwide.
Commercial trimedlure consists mainly (90-95%) of the four isomers that have the methyl and ester substituents on the ring in the trans position, denoted as A, B.sub.1, B.sub.2, and C and ca. 5-10% of the four cis-isomers. The approximate analysis of these four trans-isomers in a typical trimedlure mixture was reported to be about 35% A, 15% B.sub.1 and B.sub.2, and 50% C. At room temperature A and B.sub.1 are liquids., B.sub.2 and C solids. (McGovern et al., Journal of Organic Chemistry 31: 1472-1477 (1966a); Leonhardt et al., Journal of High Resolution Chromatography and Chromotography Communications 5: 430-431 (1982).
Two serious problems exist that prevent the most economic and efficient use of trimedlure and both are seasonally related. The first problem is that trimedlure readily forms crystals, both in storage drums and in the dental wick dispensers, during cool weather. Occasionally, crystal formation even occurs in warm weather. Agencies responsible for detecting entry into the United States of agricultural pests such as the medfly must stockpile and store trimedlure for extended periods. It must be readily available for normal survey and detection purposes as well as for the intensified trapping that is required after eradication efforts have been carried out as was recently experienced in California and Florida. When crystals form in storage containers they remain as a solid mass at the bottom of the container. The crystalline cake will not dissolve, even at summer temperatures, without a considerable amount of external heating and agitation. Crystal formation on the wick dispensers seriously interferes with rebaiting procedures. The encrusted wick cannot smoothly and rapidly absorb the applied retreatment dosage resulting in lost time and frequently in trap contamination, thereby reducing the efficiency of the trap.
The method presently used to minimize crystallization problems is costly and counterproductive. Two grades of trimedlure are currently used for survey and detection purposes, a summer and a winter grade. Summer grade is the normal isomer blend as derived from the synthesis and is prone to crystal formation. Winter grade has crystals removed prior to use and is prepared by cooling summer grade trimedlure to -5.degree. C., seeding, and then filtering off all crystals that have formed after 24 hours. This procedure results in a considerable loss of material (ca. 30-40%) and in increased costs as well as loss of the isomer most attractive to the medfly. The crystalline "sludge" that is removed to prepare winter grade trimedlure is composed mainly of the C isomer, a solid when in pure form. Field tests and olfactometer tests have shown that isomer C is the most attractive and persistent isomer (McGovern et al., Journal of Economic Entomology 59: 1450-1455 (1966b); McGovern et al., Journal of Economic Entomology, 80: 617-620 (1987), thus its artificial removal greatly reduces the efficiency of the lure. A second problem is that during the hot weather season the persistence of trimedlure is short, thus requiring frequent trap rebaitings. Because of the size of the most efficient medfly trap, the excessive volatility of trimedlure, and the maximum allowable size of the dental wick dispensers, the standard trapping procedure is to rebait a trap every two weeks during the hot season by applying a 2 ml dose of trimedlure to saturate the dispenser. Crystallization on the wick interferes with rebaiting.
McGovern et al., 1966b, supra, first proposed the use of inert (nonattractive), volatile additives which would depress the formation of the solid form of trimedlure, i.e., inhibitors of crystallization. Desirable criteria stated for an inert, volatile material are that it does not interfere with the potency of the lure and that it evaporates at about the same rate as the lure. The best of the materials tested, diethyl butylmalonate, depressed crystal formation to some extent but also reduced the attractiveness of the lure.
The authors also reported the use of pentadecanolide, a perfume fixative, as an additive that depressed the volatility of trimedlure and thereby extended the duration of effectiveness of trimedlure, i.e., an activity extender. This material was not effective in extending the activity of siglure or cue-lure [4-(p-hydroxyphenyl)-2-butanone, acetate, the attractant for the melon fly, Dacus cucurbitae Coquillett]. Because pentadecanolide is too costly for practical use, other inert, non-volatile materials were tested as activity extenders (McGovern et al., Journal of Economic Entomology 60(2): 379-383 (1967)). While several materials were found to be effective, no specific structure was found preferable for depressing the volatility of trimedlure.
Since then, a commercial product called Capilure that contains a mixture of trimedlure and extenders, has been tested and marketed. While this material extended the effectiveness of trimedlure alone, a serious deficiency of this type of system, which employs a 25% or greater quantity of a non-volatile, nonattractive ingredient, is the accumulation of this material in a dispenser of limited capacity as rebaiting occurs. An alternate choice of dispenser replacement at each treatment adds to the cost.